The invention relates to a device for supplying persons extremely hard of hearing with acoustical signals according to the introductory (generic) part of claim 1 and to devices for implementing said method. Such methods and devices are the subject matter of the German Pat. No. 29 08 999.
Known from the U.S. Pat. No. 3,385,937 is a hearing aid with a microphone for the conversion of the received acoustical signals into electrical signals of which those which are allowed to pass by filters are employed for the modulation of an electrical auxiliary alternating current, the modulated signal being then supplied, after amplification and conversion in a headset, as an acoustical signal to the ear. In this system the filters are to be designed in such manner that they only allow signals to pass whose frequencies either lie between 1500 and approximately 3500 Hz or between a first value of the range 4500 through 6000 Hz and a second value of the range 7000 through 8000 Hz and that the frequency of the electrical compensation voltage lies between 350 and 1000 Hz. That part of the signals arriving from the microphone which lies below approximately 1000 Hz can be added to such a compensation voltage or, respectively, a pair of such voltages. Such hearing aids, however, have not been able to prevail in hearing aid technology because, given only one filter, the filter width 1500 Hz through 3500 Hz is too broad and, given employment of two filters, the filter widths are too narrow and important speech information is not made available to the person who is hard of hearing.